Many copper deposits contain both sulfide and oxidized copper minerals in close association. For example, many deposits of copper sulfide minerals which occur near the ground surface are partially converted by weathering effects to mixed sulfide-oxidized ore. Also, many orebodies which were opened and originally mined as sulfide ores have over the years become partially oxidized. The sulfide minerals of such ores are readily concentrated by froth flotation, but the oxidized minerals are more difficult to concentrate.
It has been proposed many times to treat the oxidized minerals with a reactive sulfide, to convert them at least superficially to sulfide form, so that they too may be concentrated by froth flotation along with the sulfide minerals. Such proposals have met with some success, but the recovery of oxidized copper minerals by this technique has been poor. Whereas it is generally possible to recover in the flotation concentrate 70% to 90% or even more of the sulfide copper content of a mixed ore, the recovery of oxidized copper minerals is ordinarily much poorer, generally less than 50% and often less than 25%.